Strip mining is a common method of mining coal or excavating large areas of land. Therefore, strip mining operations involve the use of extremely heavy and rugged digging equipment capable of moving millions of pounds of earth. Typically, drag lines manipulate the position of a "bucket" used to dislodge, hold, and remove the soil from the site. A bucket can be virtually any size. For example, a bucket can be 35 feet long, 20 feet wide and 15 feet in depth, and weigh approximately 100,000 pounds. One end of the bucket is open with a toothed lower lip. The bucket is attached to a boom by a number of wire ropes and chains. These ropes and chains can bear the weight of the load in the bucket as well as control the orientation of the bucket.
One method of strip mining, known as "chopping," tips the bucket vertically with the toothed lip downward. The bucket is lifted several hundred feet above the ground and then allowed to free fall into the ground. The weight of the falling bucket dislodges a large quantity of soil which is then contained within the bucket. The bucket is then lifted and tilted to a horizontal orientation to prevent the soil from falling out of the bucket. The bucket is next moved to another location and tilted vertically. A dump block is an essential component in the dumping procedure. It allows for the smooth transition of forces between the hoist chains and the drag chains. It is imperative that the dump block not fail.
Prior dump block designs provide a housing around the dump block sheave. This housing consists of a pair of opposed internal plates with each attached to an external plate. The sheave is rotatably mounted around a centrally located shaft and within the housing. The external plate is generally circular with a plurality of ribs extending from a central hub to an external band. Each rib has a central portion or web of increased sectional diameter for increased strength. However, the web portion protrudes. The protruding webs often strike the dump ropes damaging the ribs and/or severing the ropes. Moreover, rocks and dirt can enter the housing between the ribs. These contaminants can jam the sheave, preventing it from rotating. The bearings upon which the sheave rests are also susceptible to failure due to the jarring impacts suffered by the dump block in use.
Therefore, a need exists for a new dump block design which minimizes the incidence and severity of impacts during use. Such a dump block should incorporate a housing with an external plate which maintains the same strength of a ribbed external plate but is less likely to impact directly with the dump ropes. In the event of an impact, the new external plate should angle off the force of the blow. Also, the external plate should minimize the likelihood of damaging the dump ropes. An improved dump block should also cushion the sheave bearings to increase their useful life.